8O VICTOR E. SHELFORD. 



A knowledge of the effect of evaporation upon animals is im- 

 portant for the following reasons: (i) Because knowledge of the 

 relationships of land animals to the surrounding medium is 

 important from the standpoint of evolution and physiology, 

 (2) because factors controlling distribution are effective in pro- 

 portion to their effect upon the organisms concerned, and (3) 

 because animals kept under laboratory conditions in experiments 

 in behavior, genetics, etc., are often subjected to constantly 

 changing atmospheric conditions and these changes may be 

 sufficiently important to interfere with the results and the 

 validity of the conclusions drawn. With these points in mind, 

 the writer and Mr. E. O. Deere undertook to construct a piece of 

 apparatus for the control of atmospheric conditions, but especially 

 to establish experimental gradients and to test the reactions of 

 animals to variations in the rate of evaporation. Various diffi- 

 culties were experienced in getting the apparatus into working 

 order and it was necessary for Mr. Deere to leave when the ap- 

 paratus was ready for the control of humidity and some half 

 dozen experiments had been performed. Nearly all of the experi- 

 ments accordingly devolved upon the writer and we present the 

 method of work only, as a joint contribution. 



II. A METHOD OF ESTABLISHING EVAPORATION GRADIENTS. 



BY VICTOR E. SHELFORD AND E. O. DEERE. 



The air supply was obtained by a compression pump as shown in Fig. i. A 

 metal funnel (MF) covered with cheese cloth conducted the air to a pipe, 14 cm. 

 in diameter and 340 cm. long, to a Beach-Russ Vacuum pump, no. i, run by a 

 one-half horse-power motor. The air left the pump through a f-in. iron pipe, 

 and entered a J-in. Crane oil separator, which removed the oil with which 

 the pump is operated. In the pipe near the oil separator there was a pressure 

 gauge, an air-cock opening to the exterior, and an automatic blow-off set for 5 Ib. 

 pressure. From here the air passed through 15 m. of f-in. galvanized iron pipe, 

 the central 5 m. of which was surrounded by a i|-in. iron pipe water-jacket, con- 

 nected with the city water supply by means of a |-in. iron pipe, provided with a 

 valve. By turning the city water supply into this jacket we were able to lower the 

 temperature of the air when the outside air was warmer than the room. This 

 was necessary because after the flows were divided they passed varying distances 

 before reaching the tanks and if the temperature of the air was higher than that of 

 the room, different amounts of cooling gave different temperatures in the experi- 

 mental boxes. Several brass ground unions made it possible to take the entire 

 line apart. The air current was divided into six parts by means of iron pipe Y 

 bends, and reduced to J-in. with bushings. Each branch was provided with a 



